This invention relates generally to video signal processing and is particularly directed to the detection of noise in a video signal.
A composite video signal is comprised of a video picture signal, a composite sync signal and a blanking signal. The composite sync signal includes horizontal and vertical synchronizing pulses which occur at predetermined horizontal and vertical scan rates and which are interspersed between the scan interval picture component in periods generally referred to as retrace intervals.
The sync signals are susceptible to various types of noise and distortion. Noise superimposed upon the composite video signal can result in excessive sync pulse amplitude variations or the breaking up, or cracking, of individual sync pulses and other undesirable modifications of the composite video signal. Such undesired variations and modifications of the sync portion of the composite video signal make it difficult to reliably recover the sync portion of the composite video signal.
Excessive noise in the composite video signal may thereby render the nondisplay portion, e.g., vertical retrace, of the signal unusable. This portion of the composite video signal is increasingly being used for the transmission of data such as in teletext and cable television (CATV) systems. In these systems, accurate detection of the vertical sync interval is essential for reliable transmission and reception of data included in the composite video signal. Noise superimposed upon the composite video signal can make recovery of data difficult due to an unreliable vertical reference.